Method of producing low core loss magnetic material



Patented July 26, 1932 UNITED STATES PATENTo FIcE ROBERT E. RENO, JR.,OF FOLLANSBEE, WEST VIRGINIA, ASSIGNOR TO FOLLAN SBEE BROTHERS COMPANY,OF PITTSBURGH, PENNSYLVANIA, A GOBPORATION OF PENN BYLVANIA METHOD 0]PRODUCING LOW CORE LOSS MAGNETIC MATERIAL Io Drawing.

My'invention relates to themanufacture of steel sheets and primarily toa novel method of making, out of alloys of iron and silicon, sheetsadapted to be used as laminae for electrical apparatus havingalternating magnetic fields, such for example as armatures for motorsand generators, and particularly for transformer cores.

A particular object of my present invention is to produce a sheet whichwhen associated with a plurality of similar sheets. in electricalapparatus of the type indicated will.

' merciallypracticable proportions of the com-.

monlyfinevitable impurities such as phosexhibit a minimum core loss. I

A further object is to provide sheets of'thei character indicated whichwillpossss: inaddition to the electrical characteristics which r formthe primary object of the invention, de sirable physical properties,such asIan 'apv manner as rerexample in an open hearth hath.The'jmo'lten iron is tapped from the preciable absence of brittleness,and a useful degree of hardness.

One preferred manner of practicing the invention will now be pointedout.

The material upon which my present process is, so far as I am aware,capable of being racticed with the best results, comprises aloys of ironand silicon in varying proportions, as follows:

For the 'armatures of relatively low powered motors, an alloy ofcommercially pure iron and .50 per cent silicon; for an improved gradeof material for the same purpose, an alloy of commercially pure iron and1.25 per cent silicon; for a still further improved grade of thismaterial, an alloy of commercially pure iron and from 1.75 per cent to2.25 per cent silicon; for a special dynamo material, an alloy ofcommercially pure iron and from 2.50 per cent to 3.50 per cent silicon;and for high wattage transformer cores of the highest grade, an alloy ofcommercially pure iron and from 3.75 per cent to 5.00 or more per centsilicon.

From the foregoing it will be apparent that my novel process hereinafterto be described may be practiced to advantage upon alloys of iron andsilicon without regard to their specific analyses. I have found theprocess results in a decrease in core loss of from .71 to .67 watt perpound at 10,000 lines and 60 cycles, in terms of the Epstein test, on aApplication filed April 18, 1930. Serial No. 445,533.

typical material analysis. Comparable reductions in core loss have beenachieved by processlng other analyses according to the principles of mynovel method, so that it is to be understood that the exact pro ortionsof iron and silicon in the material orm no part of my present invention,and the claims hereinafter are not to be limited in their application tomaterials containing the alloy elements in any specific proportions.

By the term commercially pure iron I means ingot iron having the lowestcomphorous ,'.-sulphur, manganese, carbon, and

frequently aftrace. of copper.

practicingmy present method, commercially pure iron is made in anyapproved furnace into-a ladle containing sufficient ferro-silicon toproduce the analysis ultimately desired, according to the rade of sheetdesired, as explained hereina ove.

The contents of the ladle are then teemed into molds and permitted tocool to solidity to jproduce an in ot.

he material or the sheets having been thus compounded, the manufactureof the sheets involves the following treatment: An ingot is firstcharged into a suitable reheating furnace and raised to about 2200degrees F. The ingot is then reduced in cross section by forging,rolling, or in any other convenient manner, to form sheet bar stock. Thedimensions of the sheet bar stock will obviously depend upon thedimensions of the sheets ultimately desired. A typical ultimate sheetdimension is 30 108 inches, with a thickness of 14 mils, and theinvention will be exemplified hereinafter in terms of such ultimatesheet dimensions. Accordingly, in the example supposed, the sheet barstock will be reduced to sections having a width of a about 8 inches, alength of about 31 inches, and a thickness of from to inch.

The sheet bars are next heated to bright red, or about 1600 or moredegrees F., and passed transversely through hot rolls, for about threepasses single, and one pass matched, to elongate them to about 48inches. It is to be understood that no specific number of passes is reuired in the ractice of this step, the sole unction' of this rollingoperation being to alter the dimensions of the material, to form theincomplete product known as a breakdown.

The breakdowns are conveniently matched in fours and reheated to about1500 degrees F. at which heat they are given one or more passes throughhot rolls, by which they'are ulled to about 84 inch lengths. In thiscon- 'tion the sheets are known as runovers.

The runover pack of four sheets is then doubled across its transverseaxis to become the r sheets, 42 inches in length. The pack of eightsheets is then reheated to about 1500 degrees Fiend given a suflicientnumber of passes through the rolls to attain a length somewhat in excessof pattern length, i. e., about 115 inches, for a 108 inch sheet. Itwill be remembered that the sheets of the runover pack are about 31/2-inches wide.

The object of the steps in my process thus far outlined is merely toreduce the' ingot material to sheets approximating the 'ultimatelydesired dimensions. None of these preliminar steps is thereforeessential to the practice 0 my invention, nor is the specificcombination of operations which I have used sage through a suitablecontinuous annealing furnace. It is convenient, when the continuousannealing furnace is used, to pass the ack of sheets therethrough withits doubled end leading, to avoid the risk of having the relatively limpsheets sag down between the conveying disks or rolls of the furnace. Thetemperature of the annealing furnace, and the time of ex osure of thesheets therein, are so regulate that all the sheets of the pack,including the innermost sheet, are raised to a temperature of 1450degrees F. or higher. The passage of the pack through the annealingfurnace is so regulated that the pack will leave the cooling zone at atemperature of about 700 degrees F. vI have found that this annealingstep is efiective in removing all strain from the hot rolling step andresults in giving to the sheet a gram size characteristic of theparticular alloy when normalized.

U on removal from the annealing furnace, the oubled end of the pack issheared oil, the pack is opened and pickled in any suitable picklingbath, such for example as sulphuric acid, to remove the scale on thesheets. The sheets are then washed in water and dried.

Thesheets are next given one or more passes through cold rolls merely toiron out surface inequalities and produce a truly flat sheet.

The sheets are next stacked in any convenient number on a cast steelannealing bot tom, covered with a wrought or cast steel top, which issealed against the bottom with sand. This box is then charged into asuite able annealing furnace, which is raised to a temperature ofapproximately 1650 degrees F. or higher, and while in the annealingfurnace an atmosphere of what is commercially known as carbo-hydrogengas is circulated through the box. This gas is a mixture resulting fromthe cracking of natural gas and consists of approximately 88 per centmore or less of hydrogen and 12 per cent more or less of hydrocarbons.The gas is carbonized as well as reducing. The box with its contents iskept in this condition for about nine hours or more. At the expirationof this time the box is allowed to cool in the furnace until itstemperature has been reduced to about 800 degrees F. The manner of thiscooling step I have found to be of importance, and I prefer to practiceit by merely turning off the source of furnace heat so that thetemperature of the sheets is lowered very slowly, and only by reason ofthe failure of the heat supply; not by any positive quenching means.

When the temperature has cooled to about 800 degrees F. the box is drawnfrom the furnace and an atmosphere of natural gas is circulated throughthe box until the sheets have cooled to about 300 degrees F.

When so cooled'the sheets are removed from the box and the operation iscomplete.

It is" to be understood that while I have pointed out hereinabove onepreferred manner in which the invention may be racticed, the descriptionis merely by way 0 exemplification. Numerous variations in detail tosuit individual preferences and the requirements of particular millswill readily suggest themselves to persons skilled in the art, but allsuch. modifications, to the extent that they embody the principles ofthe invention as pointed out in the appended claims, are to beconsidered within the scope and purview thereof. I I

What I claim and desire to secure by Letters Patent is:

1. The method of producing low core loss magnetic material whichconsists in reducing an alloy of iron and silicon to a sheet, am nealingthe sheet in a continuous annealing furnace at a temperature of about 1l50 F. or higher and removing the sheet from the its cooling zone of thefurnace at a temperature of about 700 F., then annealing for about ninehours at a temperature of about 1650 F. or higher in a carburizing andreducing atmosphere, then cooling the sheet in the furnace to atemperature of about 800 F. by removing the source of heat and thenfurther cooling the sheet to about 300 F. in a reducing atmosphere.

2. The method as claimed in claim 1 including the steps of pickling anddrying the sheet immediately after the first annealing step.

3. The method as claimed in claim 1 including the steps of pickling,drying, and cold rolling the sheet immediately after the first annealingstep.

4. The method of producing low core loss magnetic material whichconslsts in forming a sheet of an alloy of commercially pure iron andsilicon, normalizing the sheet at an initial temperature of about 1450F. and a final temperature of about 700 F., then annealing at atemperature of about 1650 F., and then slowly cooling the sheet. I

5. The method of producing low core loss ma etic material which conslstsin forming a s eet of an alloy of iron and silicon, normalizing thesheet at an initial temperature of about 1450 F. and a final temperatureof about 700 F then annealing at a tempera ture of about 1650 F. orhigher in the presence of a non-oxidizing gas, and then slowly coolingthe sheet. I a

6. he method of producing low core loss magnetic material which consistsin forming a sheet of an alloy of iron and silicon, norpickling,washing, cold rolling, then annealmg by subjecting the sheet to a.heating in fluence to raise its temperature to approximately 1650 F. orhigher, allowing the sheet to cool slowly to about 800 F. by removingthe source of heat, and then cooling the sheet in a non-oxidizingatmosphere to about P 11. The method of producing low cor'e lossmagnetlc material which consists in reducing an alloy containing ironandsilicon to a,

sheet, normalizing to remove from the sheet the strain' of the sheetforming operations, pickling, washing, then annealing by chargmg thesheet into a furnace having a carburizlng and non-oxidizing atmosphereand subjecting the sheet to a heating influence, then allowing the sheetto cool slowly to about 800 F. by maintaining the sheet in the furnaceand removing the source of heat, and then cooling the sheet to about 300F. in a non-oxidizing atmosphere. y In testimony whereof I aflix mysignature.

ROBT. E. RENO, JR.

malizing the sheet at an initial temperature of about 1450 F. or hi herand a final temperature of about 700 then subjecting the sheet while inthe presence of a non-oxidizing gas to a heating mfluence to raise thesheet to a temperature of 1650 F. or higher, and then allowing the sheetto cool slowly by withdrawing the heating influence.

7. The method of producing low core loss magnetic material whichconsists in reducing an alloy containing iron and silicon to a sheet,heating the sheet to a temperature of 1450 F. or'hlgher, slowly coolingto about 7 00 F., pickling, washing, then annealing at a temperature of1650" F. or higher in a non-oxidizmg and carburizing atmosphere, andthen slowly cooling to about 800 8. The method of producing low coreloss magnetic material which consists in reducing an alloy containingiron and silicon to a sheet, removing strain from the sheet, pickling,washin then annealing in a non-oxidizing and car urizing atmosphere by,raising the sheet to approximately 1650 F. or higher,

and then permitting the sheet to cool slowly.

9. The method of producing low core loss magnetic material whichconsists in reducing an alloy containing iron and silicon to a sheet,normalizing to remove from the sheet CERTIFICATE OF CORRECTION.

Patent No. 1,869,078. July 26, 1932.

' RoBERT E. RENO, JR.

It is hereby certified thaterror appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 2, lines89 and 90, for "carbonized" read carburizing; and that the said LettersPatent should be read with this correction therein that the same mayconform to the record of the case in the Patent Office.

Signed and sealed this 1st day of November, A. D. 1932.

M. J. Moore, p Acting Commissioner of Patents.

(Seal)

